In a cloud service realized in recent data centers or the like, a large number of servers are deployed, and server resources are shared with a large number of customers. Therefore, also in a network directly connected to a large number of servers that has been arranged, a redundant network is to be constructed by arranging a large number of switches and setting plural routes to increase bandwidth.
Because a switch at the previous stage of a server is in a network of layer 2, when the redundant network is constructed as it is by setting plural routes, loop configuration occurs. Therefore, it is considered to use STP (Spanning Tree Protocol) or the like. However, when using STP, there is a problem that it is impossible to increase bandwidth because the redundant routes are blocked and cannot be used for communication. Therefore, a switch which is called a Fabric switch has appeared, in which the same kind of plural switches are logically integrated. The Fabric switch can use plural lines as redundant routes by exchanging states inside. By doing so, it becomes possible to construct a redundant network with wide bandwidth without using STP. Here, Fabric represents a network that is constructed by Fabric switches.
In switches included in a Fabric, ports connecting to other switches (hereinafter referred to as inner ports) and ports connecting to servers, terminals and other network apparatuses (hereinafter referred to as outer ports) are physically fixed or are defined for each port (an inner port or an outer port is defined for each port), and it is general to construct the Fabric based on them because this Fabric switch logically and virtually integrates plural switches into one.
For example, as illustrated in FIG. 1, switches 1 to 6 are Fabric switches, and a Fabric is constructed by these switches. The switches 1 and 2 are connected to a core network, and the switches 3 to 6 are connected to servers or storages. The switches 1 to 6 are connected to each other. Then, a port illustrated by a circle on each switch represents an outer port connected to the core network or the servers, and a port illustrated by a quadrilateral on each switch represents an inner port connecting between the Fabric switches.
This is because plural lines are effectively used between inner ports, and an inner port is shown as a special interface for exchanging information inside while an outer port is shown as an ordinary switch port.
However, in a Fabric switch that physically distinguishes an inner port from an outer port, it becomes impossible not only to operate the Fabric switch but also to construct Fabric when external apparatuses are connected to inner ports, or other Fabric switches are connected to outer ports, namely, when wrong connections occur. In the example illustrated in FIG. 2, it is impossible for the switch 6 to communicate with switches 1 and 2 and to join in the Fabric, because the outer ports of the switch 6 is connected to the switch 1 and 2 that are other Fabric switches. The same is true in a case where a port to be set as an inner port is set as an outer port in the switch 6. It takes time to investigate and to handle such connection errors and setting errors.
Moreover, in a Fabric switch whose port is set as an inner port or an outer port by a definition, a setting of an inner port or an outer port is carried out individually according to configuration. For example, when all ports are set as inner ports by default, it is impossible to communicate even if the ports are connected to external apparatuses or the like because they are not outer ports. For example, as illustrated in FIG. 3, it is impossible to communicate as it is because the ports included in the port group A of the switches 1 and 2, which is connected to the core network, and the ports included in the port group B of the switches 3 to 6, which is connected to the servers, are initially set as inner ports. Therefore, initial setting processing becomes complex because the setting of the ports of the switches 1 to 6 are changed.
Furthermore, when the ports are defined as outer ports although physical connections between ports were carried out as inner ports (namely, when wrong setting occurs), it means direct connection between ports in the same switch because Fabric is logically considered to be one switch. In other words, a loop of layer 2 occurs, and it is impossible to stop the loop until the connections are removed, or the definition is modified. Moreover, when lines are connected between the outer ports due to connection error or the like although ports are set as outer ports and are scheduled to connect to external apparatuses as illustrated by thick line arrows in FIG. 4 (that is, when wrong connection occurs), a loop occurs similarly and it influences communication performance in Fabric.
When Fabric switch is applied to a large scale system, the number of switches increases, and a possibility of wrong connection and definition errors dramatically increase. Then, it is a big problem for construction of a system if the loop occurs due to the wrong connection or the definition error and a state of no communication continues for a long time by them, because it is difficult to check the Fabric.
Patent Document 1: Japanese Laid-open Patent Publication No. 11-252181
Patent Document 2: Japanese Laid-open Patent Publication No. 2000-196626